As 50% of the neurons in the brain are estimated to be inhibitory, their characterization is of import to the understanding of neuronal coding. The current proposal will investigate the development of inhibitory influences in the olfactory bulb and the effects that early sensory deprivation may have on these influences. Interestingly. studies of olfactory bulbs from normal and naris occluded developing rats indicate a decreasing number of inhibitory interneurons is associated with an increase in synaptic inhibition. We hypothesize that this paradoxical finding may be explained by changes in synaptic density throughout development or by changes in centrifugal influences, such as noradrenergic innervation, that can modify bulb inhibition. Thus. paired- pulse stimulation will be examined using an in vivo preparation to characterize the role of gamma-aminobutyric acid and norepinephrine in bulb inhibition. Plasticity in synaptic density will be determined by electron microscopy. Together, these studies will provide insights into the development of inhibitory influences in the brain and how sensory input may affect these processes.